Zero alloc: move checkmach pass before Comballoc and CSE (#1786)

backend/asmgen.ml

@@ -277,14 +277,14 @@ let compile_fundecl ~ppf_dump ~funcnames fd_cmm =
   ++ Profile.record ~accumulate:true "polling"
        (Polling.instrument_fundecl ~future_funcnames:funcnames)
   ++ Compiler_hooks.execute_and_pipe Compiler_hooks.Mach_polling
+  ++ Profile.record ~accumulate:true "checkmach"
+       (Checkmach.fundecl ~future_funcnames:funcnames ppf_dump)
   ++ Profile.record ~accumulate:true "comballoc" Comballoc.fundecl
   ++ Compiler_hooks.execute_and_pipe Compiler_hooks.Mach_combine
   ++ pass_dump_if ppf_dump dump_combine "After allocation combining"
   ++ Profile.record ~accumulate:true "cse" CSE.fundecl
   ++ Compiler_hooks.execute_and_pipe Compiler_hooks.Mach_cse
   ++ pass_dump_if ppf_dump dump_cse "After CSE"
-  ++ Profile.record ~accumulate:true "checkmach"
-       (Checkmach.fundecl ~future_funcnames:funcnames ppf_dump)
   ++ Profile.record ~accumulate:true "regalloc" (fun (fd : Mach.fundecl) ->
     match register_allocator fd with
     | ((IRC | LS) as regalloc) ->

tests/backend/checkmach/fail19.output

@@ -1,5 +1,7 @@
 File "fail19.ml", line 7, characters 5-15:
 Error: Annotation check for zero_alloc failed on function Fail19.foo (camlFail19__foo_HIDE_STAMP)
+File "fail19.ml", line 18, characters 5-26:
+  allocate 48 bytes (fail19.ml:18,5--26;dep19.ml:1,38--52)
 File "fail19.ml", line 18, characters 5-26:
   external call to caml_make_array (fail19.ml:18,5--26;dep19.ml:1,38--52)
 File "fail19.ml", line 10, characters 12-17:
@@ -15,10 +17,6 @@ File "fail19.ml", line 14, characters 46-54:
 File "fail19.ml", line 15, characters 11-20:
   allocate 24 bytes
 File "fail19.ml", line 17, characters 10-15:
-  allocate 72 bytes combining 2 allocations below
-File "fail19.ml", line 18, characters 5-26:
-  allocate 6 words
-File "fail19.ml", line 17, characters 10-15:
-  allocate 3 words
+  allocate 24 bytes
 File "fail19.ml", line 18, characters 2-27:
   allocate 24 bytes